This invention relates to a photographic bleaching solution that contains a ferric complex of an alkyliminodiacetic acid as a bleaching agent, and an organic phosphorus acid as an anti-rust agent. This invention also relates to a method of using this solution in photographic processing.
The basic image-forming process of color photography comprises the exposure of a silver halide photographic recording material, such as a film, to light, and the chemical processing of the material to reveal a useful image. The chemical processing involves two fundamental steps. The first is a treatment of the exposed silver halide with a color developing agent wherein some or all of the silver ion is reduced to metallic silver.
The second is the removal of the silver metal by the individual or combined steps of bleaching and fixing so that only dye remains in the processed material. During bleaching, the developed silver is oxidized to a silver salt by a suitable bleaching agent. The oxidized silver is then dissolved and removed from the element in a fixing step. Most commonly, a wash bath is used between the bleaching and fixing steps.
The most common bleaching agents are complexes of ferric ion and various organic ligands, of which there are dozens of possibilities, all with varying bleaching activities and biodegradability. Common organic ligands for this purpose include ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid (PDTA) and nitrilotriacetic acid (NTA).
U.S. Pat. No. 4,294,505 (Fyson) describes bleaching and bleach-fixing compositions and method using a ferric complex of one of several alkyliminodiacetic acids, which are known to be more biodegradable than other common organic ligands such as ethylenediaminetetraacetic acid (EDTA). Other bleaching agents using similar organic ligands are described in U.S. Pat. No. 5,061,608 (Foster et al) in which the bleaching agent is advantageously combined with specific aliphatic carboxylic acids to reduce dye stains. U.S. Pat. No. 5,334,491 (Foster et al) also describes similar bleaching agents in combination with specific levels of bromide ion.
DE 4,226,372 (Tappe et al) describe bleaching solutions containing excess xcex2-alaninediacetic acid (ADA) and a hydroxycarboxylic acid, such as citric acid or tartaric acid, to reduce the precipitation of iron hydroxide (that is, ferrous hydroxide or xe2x80x9crustxe2x80x9d) in the wash bath following bleaching.
It has been observed that it is unpredictable as to what materials will perform this function with any given bleaching agent. In processes utilizing methyliminodiacetic acid (MIDA) as the bleaching agent, iron-MIDA dissociation may occur in the wash bath. This rust formation must be controlled by preventing the dissociation of MIDA from ferric ion.
Thus, there is a need for specific anti-rust agents that will be effective with ferric alkyliminodiacetic acid bleaching agents without hindering bleaching efficiency.
The problems noted above have been overcome with a photographic bleaching solution comprising:
a) as a bleaching agent, a ferric ion complex of an alkyliminodiacetic acid or salt thereof, the alkyl group having from 1 to 6 carbon atoms, and
b) an organic phosphonic acid or phosphinic acid represented by one of the structures (I) or (II) below,
provided that the bleaching solution contains at least about 0.005 mol/l of ferric ion, and
further provided that the anti-rust agent is present in an amount of at least about 0.008 mol/l,
wherein structures (I) and (II) are:
R1N (CH2POnM2)2 andxe2x80x83xe2x80x83(I)
R2R3C (POnM2)2xe2x80x83xe2x80x83(II)
wherein n is 2 or 3,
R1 is hydrogen, alkyl of 1 to 12 carbon atoms, alkylaminoalkyl, alkoxyalkyl of 2 to 12 carbon atoms, cycloalkyl of 5 to 10 carbon atoms, aryl of 6 to 10 carbon atoms in the aromatic ring, or a 5- to 10-membered heterocyclic group having one or more nitrogen, oxygen or sulfur atoms in the heteroring,
R2 is hydrogen, alkyl of 1 to 12 carbon atoms, aryl of 6 to 10 carbon atoms, cycloalkyl of 5 to 10 carbon atoms in the ring, a 5- to 10-membered heterocyclic group having one or more nitrogen, oxygen or sulfur atoms in the ring, xe2x80x94POnM2 or xe2x80x94CH2R4POnM2,
R3 and R4 are independently hydrogen, hydroxy, alkyl of 1 to 12 carbon atoms or xe2x80x94POnM2, and
M is hydrogen or a water-soluble monovalent cation.
This invention also provides a method of processing a color silver halide photographic element comprising:
bleaching an imagewise exposed and developed color silver halide photographic element with the photographic bleaching solution described above.
The bleaching solution of this invention exhibits a much reduced tendency for rust formation in the processing tanks (that is, wash baths) following the bleaching tank without a loss in bleaching efficiency. Moreover, the bleaching solution is highly biodegradable and therefore avoids environmental concerns. Biogrowth is hindered in the bleach tank as well in the following processing tanks.